On many of the Cds in my library that was sent to iTunes Match... there are several songs that are not matched but just uploaded....Why would Touch match some of the songs on the CD and not all of them....Thanks
iPod touch, iOS 5.0.1
I am dealing with this as well. I have noticed three different situations for mine so far.
First, only three of the songs on one of my ripped CDs matched, the others uploaded. I notice that the actual CD I ripped is not available from iTunes, but a "Greatest Hits" CD is and it contains those three songs.
Second, only one of the songs on another of my ripped CDs uploaded, all the rest matched. For some strange reason that song is an MP3 encoded at a variable bit rate. The other songs are MP3s encoded at 192kbps. This seems to be true in many other cases as well, leading me to deduce that iTunes Match cannot match songs encoded as variable bit rate MP3s.
Third, completely unexplainable. iTunes has the album. All songs are encoded at a static bit rate. Half of them matched, half of them uploaded. These are still a mystery...
I have songs in my library encoded as variable bit rate (VBR), and they are matched. I'm curious why some other songs are not, so I'll pay attention to your other results.
This is the correct behaviour from iTunes Match. It works solely on a Song by Song basis using acoustic fingerprinting to match with iTunes Store content. If the match is above acceptable thresholds the outcome will be 'match', if not it will 'upload'.
Do you know where I can find the (equivalent of) the high level design spec for matching? Since you know about the fingerprint matching, then perhaps you have a source for a comprehensive spec. in particular, I create AAC files from cassette tapes of the days of yore. Some get matched and others do not. In some cases, I hypothesize that the track length is off by a few seconds and it therefore won't match. I have not tested this yet.
By far the most common reason for albums partially matching is because of different masterings of albums.
When albums are remastered, there are very often some fairly significant differences between different masters. An obvious difference is that very often the transitions between songs are not the same (i.e. the point where one track ends and another starts moves), but also the waveforms will be generally different and therefore match won't pick it up as the same version of the song (actually there is an argument to say that it isn't the same version of a song).
In practice, this means that these albums give a very patchy matching result, especially as iTunes generally has the newest master in the store and no others.
From my experience, this fits in very well with the actual results.
Albums purchased fairly recently tend to match very close to 100%
Older albums that have not been remastered also tend to match very close to 100%
Older albums that have been remastered since your version was produced will match very poorly (often less than 50%).
It is possible that the type of rip you have made will have an impact, but I believe that this impact will be minimal.
The result of all this is that the albums which are affected the worst are albums that are relatively popular (and have therefore warranted a remastering). That is why lots of people who report this point out that their library is fairly mainstream. If you have lots of obscure stuff then a lower proportion will have been remastered and you will probably get better results than a more mainstream library. This is the opposite of what people would assume.
Apple have not released their precise matching algorithm for public consumption, they would probably correctly view it as part of their market advantage even given the well documented apparent shortfalls.
KeithJenner, your explanation makes a lot of sense. Many thanks for taking the time to explain. I will no longer fret over the songs that don't match. Many of the songs that don't match were recorded from an album no longer in production but now part of a newer, "Best Of" compilation. I bet that many of the songs now on the "Best Of" album have been re-mastered. I have similar experience as you explain, whereby my more obscure albums match pretty well, even when recorded from vinyl onto cassette tape and then to AAC. (These cassette tapes are sometimes 35 years old!)
Not all songs Matched..Some just Uploaded
